Mortality and lamb body mass growth in free‐ranging domestic sheep – environmental impacts including lethal and non‐lethal impacts of predators

Abstract

The management and recovery of large predator populations in areas where human persecution has driven them to ecological extinction requires a solid understanding of the effects of both predation and food limitation on prey populations. We used 11 yr of data on reported losses among 17.3 million free‐ranging sheep Ovis aries in the Norwegian farming industry to elucidate the relative roles of climate, vegetation characteristics, sheep densities, lamb body mass and densities of predators and alternative prey on the number of lambs and ewes lost on summer pastures. We first examined whether predator densities predicted autumn lamb body mass through possible impacts of predators on body growth (non‐lethal effects) but found no evidence for such effects in our study system. This might be due to weak anti‐predator behavioral responses in domesticated sheep. However, autumn lamb body mass was predicted by both sheep density and winter and spring weather conditions, probably through food availability. Losses of both lambs and ewes were positively and strongly related to the density of Eurasian lynx Lynx lynx, wolverine Gulo gulo and brown bear Ursus arctos. In addition, food availability and spring weather conditions were associated to losses of lambs, while precipitation in May predicted losses of ewes. There was little evidence for interaction effects of predator species on losses, suggesting that most of the effects of the predators were additive to each other. Given the strong effect of predator densities on sheep losses, we conclude that changing livestock husbandry practices towards a system that actively protects sheep and/or active management of predator densities may be necessary to reduce sheep losses where predators are recolonizing.

Harvest models of small populations of a large carnivore using Bayesian forecasting

“…) and sheep losses in Norway are related to the size of the large carnivore population (Mabille et al. ). Harvest of carnivores is most likely to be accepted by the public if it can reduce the losses of livestock without threatening the carnivore population conservation status (Ericsson et al.…”

“…The number of lynx within a reindeer management unit in northern Sweden influenced the reindeer harvest ), suggesting that a reduction in lynx numbers would increase reindeer harvest. Similarly, losses of lambs were related to lynx population size on the county level in southern Norway (Herfindal et al 2005) and sheep losses in Norway are related to the size of the large carnivore population (Mabille et al 2016). Harvest of carnivores is most likely to be accepted by the public if it can reduce the losses of livestock without threatening the carnivore population conservation status (Ericsson et al 2004).…”

Investigating Cause-Specific Mortality of Sheep to Determine the Impacts of Carnivores on Domestic Livestock

“…Losses from predation, however, are consistently cited as the primary or contributing factor when sheep operations shut down ( Parker and Pope 1983 ;Jones 2004 ). Sheep depredation is a global issue, with recent studies showing how it affects both the sheep and predators responsible for depredations in Australia ( Allen and West 2013 ), the Patagonia region of Argentina ( Mabille et al 2016 ), and Norway ( Llanos et al 2020 ). Specific to the United States, > 50 0 0 0 0 lambs were lost to depredation in a single year at a loss of $102 million (US dollars) ( USDA 2015 ).…”